1. Field of the Invention
This invention relates generally to cleaning (treating) semiconductor substrate surfaces during the electronic component fabrication process and, in particular, to a method for cleaning the substrate surfaces during a fabrication process in which a plurality of substrates are cleaned using basic aqueous solutions of hydrogen peroxide containing specially defined complexing agents which solutions remove organic and particulate matter from the substrate surfaces and/or inhibit metal contamination of the substrate surface from the cleaning solution during the fabrication process.
2. Description of Related Art
In semiconductor cleaning technology, basic aqueous solutions of hydrogen peroxide are primarily used to contact and clean semiconductors to remove organic and particulate matter from the substrate surface. Metallic contaminants and/or organic particulate matter on the substrate surface are a problem and the well-known RCA-cleaning method is typically used for treating the semiconductor surface. In general, the RCA-cleaning method is a two-step wet cleaning cycle in which, in the first step, a basic aqueous solution of hydrogen peroxide (generally called SC-1 solution) is used to remove particles and organic contamination on the semiconductor surface. In the second step, a mixture of HCl, H.sub.2 O.sub.2 and H.sub.2 O (generally called SC-2) is used to remove metallic contaminants from the semiconductor surface.
One of the major drawbacks of the SC-1 type solutions is the contamination of the semiconductor surface with metallic ions and precipitates by adsorption and/or ion-exchange mechanisms during continuous use of the solution over a period of time in which a number of semiconductor substrates are cleaned in the same cleaning bath. This metal contamination has been shown to be responsible for certain defect formation mechanisms in subsequent device manufacturing steps. The metal contamination occurs as a result of metal ions in the SC-1 cleaning solution. The sources of the contaminating ions are impurities in the process chemicals and/or the treated wafers. Another critical problem, especially when a hydrophobic silicon surface is immersed in such a mixture, is the possibility of surface roughening by micro-masking by oxygen bubbles generated through peroxide decomposition and through localized corrosion (triggered by adsorbed metallic ions or precipitates).
To remove this metallic contamination from the surface before the next processing step, the additional acid cleaning step using the SC-2 cleaning solution is performed. This removes the metallic contamination efficiently, however, re-contamination with particles often occurs. In order to avoid these problems, it is desirable to eliminate the SC-2 acid cleaning step for a variety of reasons including cost, equipment size and cycle time reduction. To eliminate the SC-2 step, it is necessary, however, to reduce or inactivate the metal contaminants in the SC-1 cleaning step to below a specified maximum allowable activity level.
Complexing or chelating agents are known to have been added to the basic SC-1 cleaning solution to reduce the residual metal contamination on the semiconductor surface after the cleaning step. This has been shown in a number of patents including U.S. Pat. Nos. 5,290,361 and 5,302,311; European Patent Nos. 92906248.7 and 93103841.8; Japanese Patent No. PCT/JP92/00219 and German Patent No. DE3822350A1. In U.S. Pat. No. 5,290,361, a phosphonic acid complexing agent is employed in the SC-1 solution to lower or inhibit the metallic impurities left on the semiconductor surface. The patent discloses the use of a number of other chelating agents such as ethylenediamine tetraacetic acid (EDTA); 1,2-cyclohexanediaminetetraacetic acid (CDTA); triethylenetetraminehexaacetic acid (TTHA); and nitrilotriacetic acid (NTA) as not being as effective as the phosphonic acid complexants of the patent. This is also demonstrated in the article "Thin-Oxide Dielectric Strength Improvement by Adding a Phosphonic Acid Chelating Agent into NH.sub.4 OH-H.sub.2 O.sub.2 Solution" by Akiya et al., J. Electrochem. Soc., Vol. 141, No. 10, October 1994, pp. L139-L142.
The above references, however, do not address the major concern of a fabrication process which is the need for a cleaning solution which maintains its cleaning activity over a period of time during which a large number of semiconductor substrates are cleaned using the same bath. For example, in the aforementioned U.S. Pat. No. 5,290,361, known aminoacetic acid chelating agents are stated to be ineffective in SC-1 cleaning solutions when compared to the claimed phosphonic acid additives. The cleaning tests performed were concerned, however, only with a single cleaning experiment and did not address the more important problem of both bath stability and bath effectiveness over time.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide stable cleaning solutions for cleaning a plurality of semiconductor substrates with the same solution which solutions clean the surface while removing from and/or inhibiting metallic contamination of the semiconductor surface.
It is a further object of the present invention to provide a method for treating semiconductor substrate surfaces with cleaning solutions, in particular, SC-1 type solutions, which solutions remove from and/or inhibit metallic contamination of the semiconductor surface during the cleaning process in which a plurality of semiconductors are cleaned using the same solution or a replenished solution, and, further, which solutions are stable over extended use periods.
Another object of the present invention is to make the wafer cleaning process more robust in relation to accidental metal ion contamination of the solution and/or the cleaning equipment containing the solution since the presence of the complexant prevents wafer contamination and lower yields. Contaminated cleaning equipment can also be cleaned without being taken off line by using the cleaning solution of the invention.
Still other objects and advantages of the invention will be readily apparent from the following description.